Theory Of Operation

The transmission monitoring system uses three temperature sensors. If any one of the sensors fail, the other two sensors are used for the control and temperature monitoring calculations and the Malfunction Indicator Lamp (MIL) will not be illuminated. The MIL will only illuminate when more than one temperature sensor has a failure.

• The Transmission Control Module (TCM) Internal Temperature Sensor 1 is embedded in the Central Processing Unit (CPU). This sensor is normally used for over temperature shut down if the CPU temperature is excessive and for rationality monitoring.
• The TCM Internal Temperature Sensor 2 is embedded on the Printed Circuit Board (PCB). This sensor is normally used for over temperature shut down if the PCB temperature is excessive and for rationality monitoring.
• The Oil Temperature Sensor is located in the oil sump of the transmission and can be monitored with a scan tool under the Oil Temperature Sensor data parameter. This sensor is a 2-wire thermistor with a negative temperature coefficient. This means that as the temperature increases, the resistance of the sensor decreases. This sensor is normally used exclusively for the transmission control calculations.

Because of the three independent signals, it is also possible to detect which sensor caused a rationality failure. As a result the transmission can operate without any restrictions, by using one of the valid sensor signals. The sensors are not independently serviceable. If replacement of any sensor is required, the Transmission Control module (TCM) must be replaced.